The present invention relates to the manufacture of molded packings. More particularly, the invention is directed to an apparatus and method for molding packings of low-density foam or similar material for use in packaging various articles for shipment.
In the shipment of typewriters, video displays, computer terminal modules, and the like, the article must be packaged so as to protect against physical shock and vibration during handling. One technique involves the use of preformed pads or cushions that are specifically shaped to fill a portion of the space between the article and the container in which it is shipped. Typically, such pads are molded of cellular polystyrene and are placed at the ends of the article and/or above and below the article.
Such premolded pads provide only limited protection is too stiff to absorb the energy of minor shock or vibration and, since the polystyrene has almost no memory, there is little protection against a subsequent shock after the cellular structure has been crushed. Furthermore, the high temperatures and pressures required for the molding of the pads necessitate machined steel molds. Because of the high tooling costs, such pads are not used for packaging many low production items, and, generally, the pads must be centrally manufactured, stored, and transported to each packaging site.
Another packing technique involves a foam-in-place process wherein the article is placed in a container and a protective separator sheet is tucked around the article. Low-density urethane foam or similar resilient material is then poured from hand-held dispensing guns into the space between the sheet and the container to firmly support the article. The foam-in-place technique may cause undesirable stress upon sensitive portions of the article, resulting in damage, and the foam-in-place technique does not facilitate the formation of a supporting low-density foam packing below the article.
Accordingly, a related technique involves the molding of a urethane packing within the shipping container before the article is placed therein for shipment. This technique may use a mold form, generally representative of the article and any desired voids, mounted upon a platform. A separator sheet of thin plastic is placed over the mold form and drawn against the mold form by vacuum. A shipping container such as a corrugated carton with opened flaps is then placed over the mold form, and foam is injected into the container to form a molded packing directly in the container in which the article is to be shipped.
These techniques using low-density urethane foam packaging provide improved energy absortion over that of cellular polystyrene pads, and the plastic sheet provides added protection against abrasion. However, the many manual operations required and the inconvenience of molding directly in the shipping container make these techniques poorly suited to many applications. And, even when a molded packing is formed directly in the container below the article, the foam-in-place above the article may result in undesirable stress on sensitive portions of the article or inadequate support of the article. There is no convenient means to hold the separator sheet away from sensitive portions of the article and tightly against desired support surfaces during cure.
Accordingly, a need exists for a means of efficiently manufacturing molded packings, of low-density urethane foam or other resilient low-density material, that can be inserted between the article and the shipping container during packaging. Such molded packings would have the convenience of cellular polystyrene pads plus the superior energy absorption and abrasion protection of foam-in-place low-density urethane packing. In addition, the configuration of such molded packings should be controllable so as to accurately provide desired voids at sensitive portions of the article and an interference fit at desired support portions to firmly hold the article in place.
Conventional molding machines, as used in the manufacture of cellular polystyrene pads, are not suitable for molding packings of low-density urethane foam or similar material. The low-density foam lacks sufficient integrity for molding without a separator sheet of plastic or other material at the surface of the foam, and conventional molding machines cannot accommodate the sheet material. A particular problem is the difficulty of delivering a large separator sheet of thin material to a molding machine such that it can be efficiently tucked into the corners of a mold. Hand-held dispensing guns, as used in the formation of foam-in-place urethane packings described above, do not ensure a consistent, accurate flow of foam material.
It is therefore an object of the present invention to provide an apparatus and method for manufacturing molded packings of low-density urethane foam, or other resilient low-density material, for insertion between an article and a shipping container. It is a related object of the present invention to provide a means for manufacturing such molded packings accurately and efficiently without the need for expensive machined steel molds. It is a further object of the present invention to provide a means for manufacturing such molded packings that requires a minimum of human intervention and that is suited to a limited floor space. It is still a further object of the present invention to provide a sheet delivery apparatus for delivering a sheet of thin material to a molding apparatus or other sheet processing machine.